1. Field of the Invention
The present invention relates to a focal-plane shutter for camera having a first blade and a second blade.
2. Description of the Related Prior Art
Of focal-plane shutters for camera, there has been known a focal-plane shutter arranged such that two blade chambers are formed between three plate members, which are called a shutter base plate, an intermediate plate, and an auxiliary base plate, and two shutter blades called a first blade and a second blade are individually disposed in these chambers as well as a first blade actuating member and a second blade actuating member are attached to the shutter base plate outside of the blade chambers so that the first and second blades are actuated thereby. This kind of the focal-plane shutter is employed in both silver-salt film cameras and digital still cameras.
Of this type of the focal-plane shutter, there are focal-plane shutters called a locking type and a direct type depending upon a method of holding the first and second blade actuating members at an exposure actuation start position. Of these two types of the focal-plane shutters, the locking type focal-plane shutter is such that when the first and second blade actuating members are actuated to setted positions by a setting member in a setting actuation, the respective actuating members are locked at the setted positions by locking members. Accordingly, the setting member returns to an initial position instantly after it cocks the respective actuating members. In photographing, a first blade electromagnet and a second blade electromagnet, which are controlled by an exposure control circuit, sequentially release the actuating members locked by the locking members to enable the first and second blades to start an exposure actuation.
On the other hand, in the direct type focal-plane shutter, when the first and second blade actuating members are actuated to the setted positions by the setting member in the setting actuation, these actuating members cause iron piece members attached thereto to come into contact with the first and second blade electromagnets. At this time, since the respective electromagnets are not energized, the setting member does not return to the initial position instantly and stay at the setted positions. In photographing, first, the respective electromagnets are energized so as to attract and hold the respective actuating members by magnetic force, and, thereafter the setting member returns to the initial position. When the first and second blade electromagnets are sequentially deenergized by the exposure control circuit, the respective actuating members start actuation so that the first and second blades execute an exposure actuation.
As described above, in either of the types, the respective actuating members start the actuation under the control of the electromagnets, respectively in photographing. Accordingly, when malfunction occurs in the control executed by the electromagnets, the respective actuating members do not start the actuation at normal timing, and a desired proper image cannot be obtained. To cope with the above drawback, in these types of the focal-plane shutters, it is conventionally proposed and executed to provide a detecting switch with each of the actuating members to detect whether or not they start the actuation at the normal timing. It is also known that a switch for detecting the actuation of the first blade actuating member also acts a synchronous switch.
The present invention relates to a focal-plane shutter having a function for detecting the abnormal actuation of the two actuating members, in other words, the abnormal actuation of the two shutter blades and capable of being employed in both the silver-salt film camera and the digital still camera. Incidentally, in these types of the focal-plane shutters, two switch mechanisms are necessary to detect the abnormal actuations of the two actuating members. Therefore, four contact members in total are ordinarily used heretofore. However, it is advantageous to employ three contact members and to use one of the contact members by the two switch mechanisms from a view point of cost reduction. Further, these switch mechanisms are required to have durability because they are bound to be actuated each time photographing is executed as well as they are required to detect an abnormal actuation without fail only when it occurs. Thus, when the contact member that is used by the two switch members as described above is provided, it is preferable that switch mechanisms be not turned on at the same time. Further, when the dual-purpose contact member as described above is provided and arranged as a stationary contact member similar to the other two contact members, these three contact members are restricted in a layout and required to be formed in a shape devised specially. Further, there is a possibility that a layout of other shutter constituting members is effected by the three contact members. Accordingly, when the three contact members are provided, they must have a degree of freedom in the layout thereof.
An object of the present invention is to provide a low cost focal-plane shutter for camera that is excellent in durability and has a degree of freedom in a layout.
To achieve the above object, a focal-plane shutter for camera includes a first blade actuating member for causing a first blade to execute an exposure actuation in photographing, a second blade actuating member for causing a second blade to execute the exposure actuation in the photographing, and a movable contact member coming into contact with a first stationary contact member in the photographing by moving from a neutral position following the actuation of the first blade actuating member, coming into contact with a second stationary contact member after moving beyond the neutral position by being actuated in an opposite direction by the second blade actuating member, and returning to the neutral position when the respective actuating members execute a setting actuation.
In the above arrangement, the focal-plane shutter can be very preferably arranged as a focal-plane shutter for digital still camera by arranging the shutter so that photographed data starts to be transferred from an imaging device to a memory when the movable contact member comes into contact with the second stationary contact member at the time the first blade and the second blade execute the exposure actuation normally.
Further, the focal-plane shutter according to the present invention has such features that it can be manufactured at low cost by reducing the number of parts, is excellent in durability, and has a degree of freedom in a layout of respective contact members.